1. Field of the Invention:
The invention relates to a seat for a motor vehicle, wherein the seat includes a back rest arrangement, a seat cushion arrangement and an arrangement for hingedly connecting the back rest arrangement with the seat cushion arrangement. The connecting arrangement includes a double-acting drive for producing a rotary movement which takes place optionally starting from a neutral position of a drive lever into one or other direction of rotation wherein the shaft is only turned by the drive so long as the drive lever is swivelled away from its neutral position whereas, when the drive lever is swivelled towards its neutral position the shaft is not entrained. Thus, the double-acting drive is included as part of a seat adjustment device.
2. Background Information:
An adjustment drive of the type just described, having an angle adjustable component in which the gearbox axis is mounted, is known from German Patent No. 36 08 858. An adjusting wheel with entrainment flanks is connected to this gearbox axis by an adjustment device which has two oppositely acting coil springs arranged concentrically with the gearbox axis. An operating arm is mounted concentric with the gearbox axis on this angle adjustable component. The two entrainment members of the operating arm which are designed as a double-armed levers engage with a handle which is mounted on an angle adjustable component and which engages these entrainment members and swivels the operating arm.
With a rotary joint fitment along the lines of that just described, the distance between the entrainment flanks is so large that during engagement a comparatively large angular stretch has to be covered in order to make up for an idle stretch. A fine-stepped engagement is thus not possible. A switch mechanism which is free of fixed operating steps and thus operates with infinite adjustment is described in German Patent No. 41 23 103. According to this a rocker lever is rotatably mounted on the separating arm on the angle bisector of two rays passing through the gearbox axis and rotary axes of the entrainment members. On one side the rocker lever has cams which engage with rocker levers of the entrainment members in order to lift the latter out of engagement with the gearing of the ratchet wheel, and on the other side the rocker lever has a control face.
This control face contains a central concave area and convex areas adjoining the concave area on each side to include an obtuse angle between same.
The outer surface of a slide pin connected to one of the two angle adjustable parts adjoins the control face wherein the neutral position of the operating arm the outer face of the slide pin adjoins the concave area of the control face. When operating the operating arm in one or other adjustment direction the rocker lever tilts so that through this design a response is obtained even with a very slight angular movement of the operating arm.
The disadvantage of this design lies in the relatively large structural space caused by the separately mounted levers. Owing to the principle of keyed engagement using detents, or pawls, whose division cannot be kept as small as required an idle path of the drive lever cannot be completely avoided.